Molecular Cobalt Catalysts Grafted onto Polymers for ... · Efﬁcient Hydrogen Generation Cathodes Cheng-Bo Li,* Yilong Chu, Pengfei Xie, Lunqiao Xiong, Ning Wang, Hongyan Wang,

Molecular Cobalt Catalysts Grafted onto Polymers forEfficient Hydrogen Generation Cathodes

Cheng-Bo Li,* Yilong Chu, Pengfei Xie, Lunqiao Xiong, Ning Wang, Hongyan Wang,and Junwang Tang*

1. Introduction

It is anticipated that hydrogen will play a central role in thenext several decades as climate change threatens the well-beingof the planet.[1] In this scenario, the development of advancedmaterials and techniques for electro- and photoelectrocatalytichydrogen production has received increasing global attention.[2]

Molecular catalysts are attractive because the ligand environmentallows for tuning of their reduction potentials and chemical

properties. To this end, the immobilizationof soft molecular catalysts on hard electro-des is gaining interest.[3] Although someversatile strategies have been reported fortheir immobilization onto metal oxide,[4]

carbon-based,[5] and conductive electrode[6]

surfaces for applications in electro- andphotoelectrocatalytic H2 production, manysystems are confined for implementationat scale due to being designed with synthet-ically challenging, including costly ligandmanifolds (providing good stability andcatalytic properties for catalysts), difficultlinker design (considering their length,polarity, flexibility, conductivity, etc.), andnecessary anchor components. An ideal

system would require minimal synthetic effort, only inexpensivematerials, and have the capability to be directly tied to a renew-able energy source to produce clean H2 without further modifi-cation.[7] Although immobilization via drop-casting methods andother electrostatic-based deposition techniques used to affix mol-ecules to surfaces offer ease of assembly, the development ofmore precise surface attachment chemistries could offer addi-tional control over orientation of attached components, surfaceloading, passivation of the substrate, and interfacial energetics.[8]

In this article, we report polythiophene analogue (PTTB), poly-merized by 1,3,5-tri(thiophen-2-yl)benzene (TTB), as one kind ofconjugated microporous polymer networks which could serveas a surface-grafted organic coating for assembly of hydrogen-evolving molecular catalysts onto a glassy carbon (GC) electrodeor fluorine doped tin oxide (FTO) glass electrode (Scheme 1).Many thiophene-based conjugated microporous polymer net-works have been reported with excellent electrical, electrochemi-cal, and optical properties, are usually cheap, and can beconveniently prepared at large scale via chemical or electrochem-ical approaches, thus our approach provides an incredibly versa-tile option open to nearly all aromatic systems.[9] Their enlargedsurface area and rich π-bonds also provide facile platforms forimmobilization π-bond-rich molecular catalysts by π–π stackingand hydrophobic interactions. Meanwhile, the complicateddesign of linkers and anchors for molecule immobilization couldbe avoided. Especially, non-water-soluble molecular catalysts onthe fabricated electrodes would be more stable due to the lack ofcompetition dissolution into water.

Recently, we and Du’s group reported a series of metal–salencomplexes as hydrogen-evolving catalysts for homogeneousphoto- and electrocatalytic hydrogen evolution.[10] These metal–salen complexes have merits of accessibility, cost-effective

Dr. C.-B. Li, Y. Chu, P. Xie, Dr. N. WangKey Laboratory of Synthetic and Natural Functional Molecule of theMinistry of EducationThe Energy and Catalysis HubCollege of Chemistry & Materials ScienceNorthwest UniversityXi’an 710127, P. R. ChinaE-mail: [email protected]

L. Xiong, Prof. J. TangDepartment of Chemical EngineeringUCLTorrington Place, London WC1E 7JE, UKE-mail: [email protected]

Dr. H. WangSchool of Chemistry and Chemical EngineeringShaanxi Normal UniversityXi’an 710119, P. R. China

The ORCID identification number(s) for the author(s) of this articlecan be found under https://doi.org/10.1002/solr.202000281.

© 2020 The Authors. Published by Wiley-VCH GmbH. This is an openaccess article under the terms of the Creative Commons AttributionLicense, which permits use, distribution and reproduction in anymedium, provided the original work is properly cited.

DOI: 10.1002/solr.202000281

A conjugated microporous polymer is in situ electropolymerized to form a basisfor immobilization of a molecular catalyst onto glassy carbon. A cost-effectivemolecular catalyst is then grafted onto the polymer by π–π interactions asevidenced by X-ray photoelectron spectroscopy (XPS), Fourier transform infraredspectroscopy (FTIR), and UV–vis spectra. The prepared cathode represents a highactivity toward hydrogen evolution (109 100 turnovers in 2 h) in mild acidicaqueous solutions with a �100% faradaic efficiency. The cathode also shows avery good stability. In total, this article introduces a facile means to design andprepare a hydrogen generation cathode using widely available and inexpensivematerials.

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synthesis, and hydrogen-evolving performance.[11] In addition,they are electroneutral, water insoluble, and rich in π-bonds,exhibiting very good compatibility with conjugated polymersto construct composite catalyst in the current work. Therefore,this work represents a facile method toward developing an inte-grated cathode for electrocatalytic hydrogen evolution on molec-ular catalysts immobilized onto GC or FTO substrates, in whichPTTB is an excellent linker for cobalt(II)–salen complex.Furthermore, using a conjugated microporous polymer for sur-face functionalization allows use of a broad range of π-bonds,giving additional control over surface loading capacity and attach-ment stability of catalysts as new materials and discoveries.

2. Results and Discussions

Fabrication of cobalt(II)–salen complex immobilized electrodesvia a polymeric interface starts with electropolymerization ofTTB monomers to form conjugated microporous polymerPTTB on FTO or GC by cyclic voltammetry (CV) method. Thisapproach provides polymers as a thin film bearing rich π-bondsbinding sites and significantly increases the geometric arealoading capacity of catalysts on the electrode. After the polymeri-zation, wet chemical treatment of the polymer-modified surfaceusing a solution of cobalt(II)–salen complex is conducted

followed by thoroughly rinsed with corresponding solvents(Scheme 1). Fourier transform infrared spectroscopy (FTIR),X-ray photoelectron spectroscopy (XPS), and transmission elec-tron microscopy (TEM) provide consistent evidence that themolecular catalyst attaches onto the polymer surface.

2.1. Electrodeposition and Characterization of PTTB

The TTB monomers were initially polymerized by multicycledCV in anhydrous dichloromethane as the reported conditions.[9b]

Open-top polymer tubes and cauliflower-like polymer pelletscould be obtained under different CV cycles (Figure S1,Supporting Information). However, the deposited PTTB filmfractured and stripped easily after separating from the electrolytedue to the quick evaporation of dichloromethane. In another way,the PTTB polymer could be deposited in the acetonitrile, havinggood integrity and adhesion on the electrode. To uniform thepolymer samples, the CV electropolymerization process in ace-tonitrile was conducted for ten cycles (Figure 1a).

The morphological characteristics of PTTB were then charac-terized using scanning electron microscopy (SEM) and TEM.Figure 1b shows a top-view SEM image of the PTTB, showingthe morphology as a thin film. The thickness of the film wascharacterized by obtaining cross-sectional SEM images ofapproximately 223 nm (Figure 1c). The detailed morphology ofthe PTTB was characterized by TEM analysis (Figure S2,Supporting Information); PTTB exhibits a 2D agglomerated lay-ered lamellar-like morphology. In addition, a lattice spacing of0.63 nm and interplanar distance of 0.64 nm were observed inthe high-resolution TEM image. The polycrystalline nature ofPTTB was also confirmed by selected area electron diffraction(SAED) patterns (Figure S2b, Supporting Information).

FTIR spectra exhibited the vibration change from monomerTTB to PTTB (Figure 1d). The frequencies of the four absorptionbands centered in the 2800–3000 cm�1 range and the broadeningof the absorption peaks in the 900–1800 cm�1 range show thevibration of the C─H groups and C═C groups of backbone changeafter polymerization. UV–vis spectra of PTTB deposited on FTOwere further detected. The background signal of FTO wasdeducted. Two absorption regions around 340–450 nm and500–700 nm were observed, which shifted to the red directionas CV cycles increased (Figure S3, Supporting Information).

2.2. Assembly of Cobalt–Salen to PTTB

Cobalt–salen complexes can be physisorbed on PTTB depositedon an electrode substrate through the establishment of π�πstacking interactions between the π-rich backbone salen ligandsand PTTB motifs. FTIR characterization shows the formationof PTTB-cobalt(II)–salen (PTTB-Cosalen), which could beverified from the appearance of the absorption peaks in the3040–3130 cm�1 range and 1360–1485 cm�1 range (Figure 2a).These vibration signals are only existing in cobalt(II)–salenand could be ascribed to the vibration of the C─H groups andC═N groups.

The presence of intact Co complex is further confirmed byXPS (Figure 2b). Survey spectra of cobalt(II)–salen-modifiedPTTB show the presence of C, N, O, S, and Co elements of the

Scheme 1. Schematic representation of the fabrication method used toassemble modified cathodes.

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catalyst and PTTB. N 1s core-level spectra of PTTB-Cosalen showa single feature centered at 398.4 eV which should be attributedto the salen ligand. In addition, Co 2p core-level spectra ofPTTB-Cosalen show peaks centered at 778.3 eV (2p3/2) and793.5 eV (2p1/2) with the expected 2:1 branching ratio, whichare assigned to CoII.[12] Another peak with binding energies of�164.0 eV are observed for PTTB-Cosalen, which correspondsto S 2p. The broad peaks at 168.0 eV is assigned to the shakeupsatellites.[6e] The full XPS spectra of PTTB-Cosalen samples areshown in Figure S4, Supporting Information. Based on theinductively coupled plasma mass spectrometry (ICP-MS) resultsof the acidic-digested sample of PTTB-Cosalen, the Co contentwas calculated to be 1.75� 10�9 molCo cm�2.

The aforementioned data support the assembly of PTTBwith cobalt(II)–salen moieties assembled by π–π stacking. It ispredictable a planner structure of the cobalt(II)–salen benefitsthe intimate contact with the PTTB film by π–π stacking interac-tion. Furthermore, we investigated four-tertiary-butyl-derivedsalen complex (cobalt(II)–tBu–salen) to backward this viewpoint.The XPS analysis (Figure S5, Supporting Information) of PTTB-cobalt(II)–tBu–salen (PTTB-Co(tBu–salen)) shows a much lowerCo:S (1:72) than that in PTTB-Cosalen (1:9).

2.3. Electrochemistry Studies

The electrochemistry of GC/PTTB-Cosalen was investigatedby CV. Maximum average surface catalyst concentrations of1.69� 10�10 molCo cm�2 are estimated from the integration of

Figure 1. a) Cyclic voltammograms (ten scans at 200mV s�1) of the monomer TTB in 0.1 M Bu4NClO4/MeCN. b) SEM image of PTTB electrodepositedby CV. c) SEM cross-sectional image of a GC/PTTB electrode. d) FTIR transmission spectra of TTB (black), PTTB before (red).

Figure 2. a) FTIR transmission spectra of Cosalen in KBr (black), PTTBin KBr (blue), and PTTB-Cosalen in KBr (red). b) Survey (up) and Co2p core-level (down) spectra of pristine PTTB (black) and PTTB-Cosalen (red) supported on GC substrates.




the electrochemical wave (Figure S6, Supporting Information).This value is approximately 1/10 of that obtained from ICP-MSmeasurements of the sonicated and digested PTTB-Cosalen, sug-gesting that the majority of the cobalt centers are electrochemi-cally inactive. The hydrophobic property of PTTB may impedethe reaction of deep-seated Cosalen with water.

The new molecular-based GC/PTTB-Cosalen material iscatalytically competent for H2 evolution from fully aqueouselectrolytes at a mild pH. A CV experiment recorded on aGC/PTTB-Cosalen electrode (Figure 3a, red solid line) was firstconducted in acetate buffer solution (0.1 M, pH 4.5). A strongwave with a cathodic onset potential of Eonset¼�0.45 V versusreversible hydrogen electrode (RHE) is observed as a result ofcatalytic reduction of protons to H2. Testing of the sameGC/PTTB electrode in identical conditions prior to catalystadsorption showed minimal background current (Figure 3a,black solid line), confirming this activity as being directly a resultof the catalyst’s presence. We also tested the linear sweep voltam-metry experiment recorded on a GC/PTTB-Co(tBu–salen) elec-trode, a much weaker cathodic wave was observed (Figure 3a,blue solid line), indicating the branched molecular catalyst isnot suitable for the GC/PTTB substrate due to the limitedπ�π interaction. Indeed, several other well-known catalysts suchas μ-(1,3-propanedithiolato)-hexacarbonyldiiron (pdt-Fe2S2),

[13]

cobalt diimine�dioxime complex (Co(DO)(DOH)pnBr2),[14]and cobalt tetraphenylporphyrin (CoTPP)[15] were also assembledto form a GC/PTTB-catalyst electrode, albeit with much poorercatalytic performance (Figure S7, Supporting Information)due to either low amount loaded or hard to load. The loadingamounts of Cosalen effect related different assembly time are

shown in Figure S8, Supporting Information, in which the10 h assembly sample shows the highest catalytic current likelydue to the highest amount of Cosalen loaded. Furthermore, O2tolerance of GC/PTTB-Cosalen was investigated in acetate buffer(pH 4.5, 0.1 M) by linear sweep voltammetry (LSV) scanning withair bubbling or N2 protection (Figure 3b). Results revealed thatO2 had very limited impact on effectiveness of proton reductionby the grafted molecular catalyst which still displays good activityfor H2 evolution in the presence of O2, indicating an excellentselectivity to proton reduction against O2 reduction.

As the pH of the aqueous solution is lowered, an increasein current is observed (Figure S9, Supporting Information).A potential value of �0.63 V versus RHE was required to reacha current density of 1 mA cm�2 at pH 4.5. Tafel analysis(Figure S10, Supporting Information) gave a Tafel slope of193 mV per decade and an exchange current density of10�6.3 A cm�2 geometric. This value is comparable with thatreported for MWCNT/[Co(DO)(DOH)pnBr2] (10

�6.5 A cm�2

geometric)[5a] and electropolymerized of Co(II) dibenzotetraazaannulene (CoTAA, 10�8 A cm�2 geometric).[16]

Controlled potential electrolysis (CPE) of GC/PTTB-Cosalenin acetate buffer solution (0.1 M, pH 4.5), measured at �0.75 Vversus RHE, consumed 7.13 coulombs of charge after 2 h(Figure 3c,d). Although a broad current density was observeddue to the bubbles generated on the electrode surface andtheir desorption matter, the current density stabilized after 2 hat a constant value of approximately 1 mA cm�2. Analysis ofthe gas mixture in the headspace (Figure S11, SupportingInformation) of the working compartment of the electrolysis cellby gas chromatography confirmed production of H2 with a

Figure 3. a) CV measurements recorded on a GC/PTTB-Cosalen electrode (red line) compared with that of GC/PTTB-Co(tBu–salen) (blue line) andan unfunctionalized GC/PTTB electrode (black line) in acetate buffer (0.1 M, pH 4.5) at 100mV s�1. b) Oxygen resistance investigation run on aGC/PTTB-Cosalen in acetate buffer (0.1 M, pH 4.5). c) Evolution of the current density during an electrolysis experiment run on a GC/PTTB-Cosalen electrode (red dotted line) compared with that of a blank GC/PTTB electrode (black dotted line) at �0.75 V versus RHE in acetate buffer(0.1 M, pH 4.5). d) Charge passed during the same experiment for electrocatalytic H2 production.




Faradaic yield of approximately 100%. Considering that two elec-trons are required for the formation of a H2 molecule and usingthe loading concentration of the catalyst (1.75� 10�9 mol cm�2)and the active surface concentration of the catalyst(1.69� 10�10 mol cm�2), we calculated a turnover number(TON) of 10 540 and 109 100, respectively. A turnover frequency(TOF) per grafted Co catalyst of 1.5 and 15.2 s�1 was calculated.The bulk electrolysis was then conducted under �0.6 V versusRHE. After 20 h electrolysis, the current density still retained60% of the initial, indicating a very robust cathode (Figure S12,Supporting Information). Although the stability is not compara-ble with those reported in inorganic materials,[17] its activity issuperior to most of other obtained molecular catalyst-graftedelectrodes (Table 1).[5c,d,f,g,6b,18]

XPS analyses of GC/PTTB-Cosalen after electrochemical stud-ies display peaks similar to the ones observed before electrolysis,suggesting that the material left on GC is stable under reductiveand acidic conditions (Figure S13, Supporting Information). Inthe Co region, the two broad sets of signals that correspond to the2p3/2 and 2p1/2 core levels are still observed. The absence of anypeak below 780.9 eV excludes the presence of cobalt oxide ormetallic cobalt on the surface. This observation clearly excludesany reductive transformation of the grafted molecular complexinto the nanoparticle H2–CoCat material as reported molecularcomplexes in solution.[19] The ICP-MS analysis of PTTB-Cosalensample after 2 h electrolysis (�0.75 V vs RHE) showed that about44% Cosalen still retained on the electrode (Table S1, SupportingInformation).

3. Conclusions

We demonstrate here, for the first time, a cobalt–salen catalystwas grafted onto electropolymerized conjugated microporouspolymer PTTB, which generated a very active electrocatalyticcathode for H2 production from mildly acidic aqueous solutions.The electrode was cost-effective, efficient, and robust with a goodstability. Around 109 100 turnovers were obtained during 2 h ofelectrolysis in an acetate buffer at a potential of �0.75 V versusRHE. The high catalytic activity also remained under O2 expo-sure, proving an excellent selectivity to proton reduction. Withthe wide range of conjugated microporous polymer substratesand π-rich molecular catalysts available for deposition, a varietyof materials for heterogeneous dihydrogen-generation catalysiscould be developed, giving substantial possibility for materials

engineering. Applications in photoelectrocatalytic systems areof particular interest, and corresponding studies are underway.

4. Experimental Section

Materials: 1,3,5-Tri-(thiophen-2-yl)benzene (TTB), salicylaldehyde, anhy-drous dichloromethane, acetonitrile, ethanediamine, and Co(Ac)2·6H2Owere purchased from Adamas Company (Shanghai, China).Tetrabutylammonium perchlorate (Bu4NClO4) was obtained from Aladdin(Shanghai, China). HAc buffer solutions were prepared by mixing 0.1 MHAc and 0.1 M NaAc. Cosalen complexes were prepared as previouslyreported methods.[10a,b,d] All reagents were used without further purification.

Electropolymerization: All of the electropolymerization experimentswere performed on a CHI600E electrochemical workstation (Chenhua,Shanghai, China) using a three-electrode system. Dichloromethane or ace-tonitrile solution (5mL) containing 5mMmonomers and 0.1 M Bu4NClO4was added to a glass electrochemical cell. Glassy carbon rods (diameter3 mm), glassy carbon sheet (1� 2 cm2), SEM electrode (glassy carbon,diameter 3 mm), and FTO (1� 2 cm2, square resistance 5–7Ω) were usedas working electrodes, in combination with a platinum counter electrodeand an Ag/Agþ electrode as the reference electrode. Electro polymeriza-tion was performed by CV method was performed from �0.7 to 2.0 V at ascan rate of 200mV s�1 with different scan numbers.

Electrode Fabrication: Glassy carbon substrates were first polished withpolishing alumina, followed by flushing with water and ethanol, and thenwere sonicated in ethanol before use. The cleaned glassy carbon sub-strates were then used for deposition of PTTB by CV. When an FTO ora glassy carbon sheet was used as working electrode, the surface was con-trolled to expose 1� 1 cm2 by covering tape. The polymer-grafted electro-des were rinsed thoroughly with dichloromethane or acetonitrile and driedunder air; afterward dipped in 1 mM Cosalen methanol solution for 10 h toassemble the molecular catalyst, which were then rinsed with methanolthoroughly and dried under air. FTO used as substrate to grow PTTBwas first sonicated in isopropanol, water, and ethanol in sequence forcleanliness, followed by polymer deposition and catalyst assembly as per-formed on glassy carbon substrates.

Electrochemical Methods for Hydrogen Evolution: Electrochemistryexperiments were conducted using a CHI 600E. The LSV and CV measure-ments were conducted in a three-electrode configuration electrochemicalcell (1 chamber) under an inert nitrogen atmosphere using the fabricatedglassy carbon rods as the working electrode, a platinum wire as the auxil-iary (counter) electrode, and an Ag/AgCl/3 M KCl electrode as the refer-ence electrode. The Ag/AgCl electrode was calibrated with a reversiblehydrogen electrode (see Figure S14, Supporting Information). The poten-tials in electrocatalytic hydrogen evolution studies were converted to RHEby adding a value of (0.186þ 0.059 pH) V.

CPE measurements to determine Faradaic efficiency and study long-term stability were conducted in a sealed two-chambered H cell wherethe first chamber held the glassy carbon sheet working electrode andAg/AgCl reference electrode in 50mL of 0.1 M HAc/NaAc buffer (aq) atthe corresponding pH, and the second chamber held the auxiliary elec-trode in 50mL of 0.1 M HAc/NaAc buffer (aq) at the corresponding pH.The two chambers, which were both under a N2 atmosphere, were sepa-rated by a proton exchange membrane. Continuous stirring was con-ducted during the electrolysis to get rid of the bubble adhering on thesurface of the fabricated electrode. The amount of hydrogen producedwas quantified by gas chromatography. The faradaic efficiencies werecalculated using the following equation:

Faradic yield ¼ 100� 2F½H2�Q

(1)

where F is the Faraday constant (C mol�1), [H2] (mol) is the amount ofhydrogen measured in the headspace, and Q (C) is the charged passedduring electrolysis.

Table 1. Electrocatalyic proton reduction in aqueous solution usingelectrodes modified with molecular catalysts.

Electrode TON TOF [h�1] Ref.

PTTB-Cosalen 1.1� 105 5.5� 104 –CNT/Ni(P2phN

2CH2pyrene

)2 8.5� 104 1.4� 104 [9]CNT/pPyCo 420 42 [10]

CNT/Ni(P2phN2CH2

)2 1� 105 1� 104 [12]RGO/Co(S2C6H2Cl2)2 9.1� 106 1.1� 106 [13]GC/CoTPP 26 17 [15]




TON ¼ number of H2 moleculesnumber of catalyst molecules

(2)

TOF ¼ TONelectrolysis time

(3)

Physical Methods: FTIR spectra were acquired using a Bruker INVENIOR spectrometer. Samples for analysis were mixed into a KBr matrix andpressed into pellets. The samples for FTIR were collected by peelingoff the films on the hard electrodes. UV–vis absorption spectra weremeasured with a Cary 60 UV–vis spectrophotometer.

To measure the catalyst loading, ICP-MS was performed using anAgilent 7900 ICP-MS. A 0–100 ppb cobalt standard in nitric acid(Sigma-Aldrich) was used to construct a calibration plot. The ICP-MS sam-ples were prepared by immersing a GC/PTTB/Cosalen wafer into 5mLaqua regia solution, followed by sonicating the solution for 1 h. The solu-tion was then diluted to 50mL with deionized water. The Co concentrationin the solution was analyzed by ICP-MS and was converted to the Cosalenwith the same quantities. The maximum Cosalen concentration on theelectrode was then calculated from the acquired Cosalen amount dividedby the exposed area of the electrode. Following CPE experiments, the pH4.5 solutions were collected, filtered, and analyzed by ICP-MS to determineif any cobalt material was solubilized during the experiment. Relative sol-vents were analyzed as controls. The trace amounts of cobalt in these con-trols were averaged and subtracted from the cobalt concentrations.

XPS data were collected using a PHI5000 VersaProbeIII XPS instrument(ULVAC-PHI). The monochromatic X-ray source was the Al Kα line at1486.6 eV, directed at 45� to the sample surface. Low-resolution surveyspectra were acquired between binding energies of 0–1100 eV. Higher-resolution detailed scans, with a resolution of �0.1 eV, were collectedon individual XPS lines of interest. The XPS data were analyzed using aMulitpak software. The samples for XPS were prepared by peeling offthe films on the hard electrodes.

The surface morphology of the substrates was characterized using afield emission scanning electron microscope (Hitachi SU8010, Japan).Samples on SEM electrode were used to watch the morphology. Cross-sectional SEM was performed with samples on glassy carbon sheetand was obtained after depositing a protective layer of Pt. TEM was con-ducted on a Talos F200X microscope (USA). Samples for TEM were firstfabricated on FTO, and then collected in ethanol, followed with sonicatingfor 10min.

The amount of gaseous H2 was detected and quantified by headspacegas analysis after electrolysis using an Agilent 7890A Series gas chroma-tography equipped with a 5 Å molecular sieve column (Ar carrier gas at aflow rate of approximately 3 mLmin�1).

Supporting InformationSupporting Information is available from the Wiley Online Library or fromthe author.

AcknowledgementsThis work was supported by Research Plan-Science & TechnologyDepartment of Shannxi Province (grant no. 2017JQ2012), Natural ScienceResearch Program Education Department of Shaanxi Province (grant no.15JK1708), and Shaanxi Key Research grant (China, 2020GY-244). J.T.thanks EPSRC (EP/S018204/2) and Royal Society-Newton AdvancedFellowship grants (NA170422 and NAF\R1\191163).

Conflict of InterestThe authors declare no conflict of interest.

Keywordscobalt, electrochemical hydrogen evolution, molecular catalysts, polymers

Received: June 5, 2020Revised: July 22, 2020

Published online:

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Molecular Cobalt Catalysts Grafted onto Polymers for Efficient Hydrogen Generation Cathodes1. Introduction2. Results and Discussions2.1. Electrodeposition and Characterization of PTTB2.2. Assembly of Cobalt-Salen to PTTB2.3. Electrochemistry Studies

3. Conclusions4. Experimental Section

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Molecular Cobalt Catalysts Grafted onto Polymers for ... · Efﬁcient Hydrogen Generation Cathodes Cheng-Bo Li,* Yilong Chu, Pengfei Xie, Lunqiao Xiong, Ning Wang, Hongyan Wang,